170 



SCIENTIFIC NE^VS. 



[Oct. 1st, I a 



more forcibly the grandeur and far-reaching importance of 

 those generahsations which are the outcome of the highest 

 scientific work, and which are so profoundly affecting 

 modern thought. 



The Cost and Value of Food. — In a paper read by 

 Professor Atwater at the recent meeting of the American 

 Association for the Advancement of Science, he made a 

 comparison of the physiological with the pecuniary economy 

 of food. He reminded his audience that the cheapest food 

 is that which furnishes nutrition at the lowest cost, but that 

 the most economical food is that which is at once the 

 cheapest to buy and the best adapted physiologically to the 

 wants of the consumer. He then pointed out that, as a 

 rule, vegetable foods are cheaper than animal food, but are 

 not so highly nutritive. Flour is dearer to buy than 

 potatoes, but taking into account their physiological value, 

 the potatoes are less economical, because the proteid (the 

 albuminous constituent) they contain is inferior and less 

 digestible. In America, he said, the greatest waste occurs 

 with beef, lamb, veal, fish, flour, potatoes, and fruit ; but 

 there is good reason to suppose that these articles of food are 

 just as much wasted in many European countries. The 

 waste of food in our own homes is indeed proverbial, and 

 it is especially striking if account be taken of the small 

 proportion which the food actually eaten bears to the total 

 weight bought, or even to the net weight after being 

 cooked. There is little doubt that nearly all classes buy 

 more than they need, and what they buy is often badly 

 selected for the physiological ends in view. 



A large excess is actually thrown away, and when we 

 add to this the loss due to careless storing, bad cooking, and 

 unskilful use, some idea may be formed of the enormous 

 waste which is going on. As bearing on this question, we 

 remember hearing one of our largest makers of mustard 

 state somewhat paradoxically that the extent of his business 

 depended much more on the quantity of mustard unused 

 than on that consumed. Great, however, as is the financial 

 loss, Prof. Atwater considers the physiological waste still 

 greater, and he is of opinion that more harm is done by 

 unwise eating and drinking than can be estimated. The 

 rich, he saj's, suffer both in health and purse, but the poor 

 suffer most of all, because the food of the labouring classes 

 is relatively large in amount and costly in kind. Again, 

 costly materials are used when less expensive would do as 

 well, and false economy is practised in buying what seems 

 to be cheap, but is in reality dear. It should be remembered, 

 too, that all food wasted enhances the price of the food 

 actually consumed, for it costs as much to produce food 

 which is wasted as that which is used, and the total cost of 

 production has to be borne by the proportion of food 

 eaten. That plenty often makes waste is within the ex- 

 perience of all of us, but that is only a greater reason 

 why we should use every endeavour to prevent its con- 

 tinuance. 



Thermo-Electricity. — It has long been known that 

 an electric current can be produced by heating the point of 

 contact of two dissimilar metals. For instance, if a piece of 

 bismuth and a piece of antimony be soldered together, and 

 if the unsoldered ends be connected with a copper wire, a 

 current will be set up on the soldered ends being heated. 

 Thermopiles consisting of several pairs of metals joined 

 together in series have been constructed on this principle, 

 but their efficiency is extremely low, and to produce a 

 current suitable for electric lighting, it would not only be 

 necessary to have a large number of batteries to obtain the 

 electro-motive force required, but the expenditure of fuel 

 would be excessively high for the current produced. For 

 practical purposes, therefore, it is better to use a dynamo- 

 electric machine, or acid batteries. For the latter, the 

 renewal of the acid involves much trouble and expense, and 

 for the former, engine power is required. It is, however, 

 admitted by competent authorities that with the best steam- 

 engine and boiler only ten per cent, of the heat energy of 

 the fuel is converted into useful work at the engine. There 

 is then a further loss of power in the dynamo itself, and 

 roundly it may be said that, with the best boiler, engine, and 

 dynamoj only about one-twelfth of the heat energy of the 

 fuel burnt is converted into electrical energy. 



Mr. Edison has just devised an apparatus by which he 

 claims to have made a considerable step forward in the 

 direct conversion of heat into electricity. He abandons the 

 ordinary thermopile, which has such a low efficiency, and 

 he calls to his aid the fact that the magnetisation of the 

 magnetic metals is strongly affected by heat. In the ap- 

 paratus he has recently brought to the notice of the 

 American Association there are eight electro-magnets, each 

 having a hollow core or keeper of sheet iron. These 

 cores are successively heated and cooled, and in this way a 

 magnetic current is set up in each, one after the other, and 

 it is for this reason that the apparatus is called a pyro- 

 magnetic generator of electricity. The cores are heated by 

 the products of combustion of a fire below, and they are 

 cooled bj' a current of cold air drawn in by the chimney 

 draught. The idea is certainly ingenious, but the subject 

 is an extremely complex and difficult one to deal with, and 

 what the outcome of it may be it is too soon to conjecture. 

 Doubtless careful trials will be made, and we sincerely 

 trust that it may be proved that we are nearer the sqlution 

 of one of the greatest questions of the day — the direct 

 conversion of heat into electricity without excessive loss or 

 expense. 



Science in the United States. — In commenting on the 

 recent meeting of the American Association, the Neiv York 

 Tribune draws attention to the increasing importance of 

 science in daily life, and to the fact that this is now gene- 

 rally acknowledged to be the case. To the popular under- 

 standing, scientific agriculture used to be thought a mere 



